This invention relates to silicone-modified epoxy or phenolic resin compositions which cure into products having both the flexible and impact resistant properties of silicone resins and the adherent, heat resistant and humidity resistant properties of epoxy or phenolic resins. It also relates to semiconductor devices coated or sealed with the cured product of the resin compositions.
Epoxy resins and phenolic resins have good adhesion, heat resistance and humidity resistance and find use in a wide variety of applications including adhesives and paints, and recently in advanced applications such as encapsulants for semiconductor devices. However, these resins have the drawbacks of being rigid and brittle and cannot be used in hostile environments as encountered in automobiles and aircraft.
To date, extensive efforts have been made to make flexible cured products of epoxy resins and phenolic resins. For example, the inventors proposed the use of modified epoxy or phenolic resins which have been reacted with silicone (see JP-B 61-48544, JP-B 62-36050, JP-B 63-63807). This approach is to control the compatibility between an epoxy or phenolic resin as the main component and a silicon as the modifying component so as to form a phase separation structure. If the phase separation structure is an adequate microstructure, it serves to absorb impacts, contributing to improvements in the flexibility and strength of cured resin. However, this approach is among the concept of stress reduction and does not reach the flexibility level of silicone resins.
On the other hand, silicone resins achieve levels of adhesion, heat resistance and humidity resistance which are far below those of epoxy and phenolic resins.
Therefore, an object of the invention is to provide a resin composition comprising a silicone-modified epoxy or phenolic resin which cures into a product having both the adherence, heat resistance and humidity resistance characteristic of epoxy resins or phenolic resins and the flexibility and impact resistance characteristic of silicone resins. Another object is to provide a semiconductor device coated or sealed with the cured product of the resin composition.
We have found that a satisfactory silicone-modified epoxy resin or silicone-modified phenolic resin is obtained by reacting an epoxy resin or phenolic resin having in a molecule at least two structural units of the following formula (1) with an organopolysiloxane having the following average compositional formula (2). The modified epoxy or phenolic resin is such that after the modified epoxy or phenolic resin is cured alone to form a cured product or after the modified epoxy or phenolic resin is added to another epoxy resin and/or phenolic resin and cured together to form a cured product, the organopolysiloxane component does not form a phase separation structure in the cured product. This modified epoxy or phenolic resin cures into a product having both the adherence, heat resistance and humidity resistance characteristic of epoxy resins or phenolic resins and the flexibility and impact resistance characteristic of silicone resins.
Specifically, the invention provides a resin composition comprising a silicone-modified epoxy resin or silicone-modified phenolic resin obtained by reacting an epoxy resin or phenolic resin having in a molecule at least two structural units of the following formula (1) with an organopolysiloxane having the following average compositional formula (2), the modified epoxy or phenolic resin being such that after the modified epoxy or phenolic resin is cured alone to form a cured product or after the modified epoxy or phenolic resin is added to another epoxy resin and/or phenolic resin and cured together to form a cured product, the organopolysiloxane component does not form a phase separation structure in the cured product. 
Herein R3 is hydrogen or glycidyl and R4 is hydrogen or a monovalent hydrocarbon group having 1 to 6 carbon atoms.
(R1)a(R2)bSiO(4xe2x88x92axe2x88x92b)/2xe2x80x83xe2x80x83(2)
Herein R1 is selected from the class consisting of a hydrogen atom, a hydroxyl group, an alkoxy group, an alkenyloxy group, and a monovalent organic group containing an amino, epoxy, hydroxyl or carboxyl group, R2 is a substituted or unsubstituted monovalent hydrocarbon group, letters a and b are positive numbers satisfying 0.001xe2x89xa6axe2x89xa61, 1xe2x89xa6bxe2x89xa62.5 and 1xe2x89xa6a+bxe2x89xa63, the number of silicon atoms in a molecule is an integer of 2 to 1,000, and the number of functional groups R1 directly attached to silicon atoms in a molecule is an integer of at least 1.
The invention also provides a semiconductor device comprising a semiconductor chip whose surface is coated or sealed with the resin composition in the cured state.
The silicone-modified epoxy resin or silicone-modified phenolic resin used herein is obtained by reacting an epoxy resin or phenolic resin having in a molecule at least two, preferably 2 to 10, and more preferably 2 to 5, structural units of the formula (1) with an organopolysiloxane having the average compositional formula (2).
The epoxy resin or phenolic resin serving as a raw material for the silicone-modified resin should have at least two structural units of the following formula (1) in a molecule. 
Herein R3 is hydrogen or a glycidyl group represented by 
and R4 is hydrogen or a monovalent hydrocarbon group having 1 to 6 carbon atoms.
The monovalent hydrocarbon groups represented by R4 are those of 1 to 6 carbon atoms, preferably 1 to 3 carbon atoms, for example, alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, pentyl, neopentyl, hexyl and cyclohexyl, alkenyl groups such as vinyl, allyl, propenyl and butenyl, aryl groups such as phenyl. Also included are halo-substituted monovalent hydrocarbon groups in which some or all of the hydrogen atoms on the foregoing hydrocarbon groups are substituted with halogen atoms.
At least two structural units of formula (1) should be included for the following reason. When the epoxy or phenolic resin is reacted with an organopolysiloxane, either one of R3 and R4 in formula (1) reacts with functional groups R1 in formula (2). If only one structural unit of formula (1) is included and R3 reacts with the functional group R1, then the epoxy group or phenolic hydroxyl group is eliminated from the site of formula (1), and so the resin loses the function of epoxy or phenolic resin. If only one structural unit of formula (1) is included and R4 reacts with the functional group R1, the resulting reaction product has both an epoxy or phenolic hydroxyl group and an organopolysiloxane attached to a common benzene ring so that reactivity lowers due to the steric factor. In contrast, in the event where two or more structural units of formula (1) are included, if the ratio of the epoxy or phenolic resin and the organopolysiloxane blended is controlled, there is a possibility that either one of the epoxy or phenolic hydroxyl group and the organopolysiloxane be present on some benzene rings, that is, a possibility to maintain reactivity. As compared with the inclusion of one structural unit of formula (1), the inclusion of two or more structural units of formula (1) leads to a silicone-modified resin having an increased number of functional groups, resulting in a cured product having an increased crosslinking density and hence, improved mechanical strength, heat resistance and humidity resistance.
Of the epoxy resins and phenolic resins described above, those of the following formulae (3), (4) and (5) are desirable. 
Herein R3 is hydrogen or glycidyl: 
R4 is hydrogen or a monovalent hydrocarbon group having 1 to 6 carbon atoms,
R5 is xe2x80x94CH2xe2x80x94 or 
R6 is 
letters n and m are integers of at least 0.
Illustrative examples of the epoxy resins and phenolic resins of the formulae (3), (4) and (5) are compounds of the following structures. 
Herein R3 is hydrogen or glycidyl: 
R7, which may be the same or different, is hydrogen or an alkenyl group such as vinyl, allyl or propenyl, R8, which may be the same or different, is 
or 
letters n and m are integers of at least 0.
The molecular weight of the epoxy and phenolic resins is not critical although a lower molecular weight is desired for reducing the viscosity of silicone-modified resins and improving the processing of resin compositions. Specifically, it is desired that m is 0 to 5 and n is 0 to 10, and more desirably, m is 0 to 3 and n is 0 to 5 in the event where R5 is xe2x80x94CH2xe2x80x94, or n is 0 to 3 in the event where R5 is 
Another raw material for the silicone-modified resin used herein is an organopolysiloxane having the following average compositional formula (2).
xe2x80x83(R1)a(R2)bSiO(4xe2x88x92axe2x88x92b)/2xe2x80x83xe2x80x83(2)
Herein R1 is a hydrogen atom, a hydroxyl group, an alkoxy group, an alkenyloxy group or a monovalent organic group containing an amino, epoxy, hydroxyl or carboxyl group. R2 is a substituted or unsubstituted monovalent hydrocarbon group. Letters a and b are positive numbers satisfying 0.001xe2x89xa6axe2x89xa61, 1xe2x89xa6bxe2x89xa62.5 and 1xe2x89xa6a+bxe2x89xa63. The number of silicon atoms in a molecule is an integer of 2 to 1,000, and the number of functional groups R1 directly attached to silicon atoms in a molecule is an integer of at least 1.
The amino-containing monovalent organic groups represented by R1 include alkyl groups having an amino or N-substituted amino group substituted thereon, as exemplified below. 
Herein k is 1, 2 or 3.
The epoxy-containing monovalent organic groups represented by R1 include alkyl groups having a glycidyloxy or 3,4-epoxycyclohexyl group substituted thereon, as exemplified below. 
Herein k is 1, 2 or 3.
The hydroxyl-containing monovalent organic groups represented by R1 include alkyl groups having a hydroxyl or hydroxyphenyl group substituted thereon, as exemplified below. 
Herein k is 1, 2 or 3 and r is 0, 1, 2 or 3.
The carboxyl-containing monovalent organic groups represented by R1 include terminally carboxyl-substituted alkyl groups, as exemplified below. 
Herein x is an integer of 0 to 10.
In addition to the substituted organic groups mentioned above, the functional groups R1 are hydrogen, hydroxyl, alkoxy and alkenyloxy groups. Of these, the hydrogen atom and hydroxyl group bond with a silicon atom to form a hydrosilyl (SiH) group and silanol (SiOH) group, respectively.
Of the alkoxy groups, those having 1 to 8 carbon atoms, especially 1 to 4 carbon atoms are preferred. Examples include straight, branched and cyclic alkoxy groups such as methoxy, ethoxy, iso-propoxy, n-propoxy, sec-propoxy, n-butoxy, sec-butoxy, iso-butoxy, tert-butoxy, n-pentyloxy, sec-pentyloxy, cyclopentyloxy, n-hexyloxy, and cyclohexyloxy. Preferred alkoxy groups are of the following formula. 
Herein k is 1, 2 or 3.
Of the alkenyloxy groups, those having 2 to 6 carbon atoms, especially 2 to 4 carbon atoms are preferred. Exemplary alkenyloxy groups include vinyloxy, propenyloxy, isopropenyloxy and isobutenyloxy.
R2 stands for substituted or unsubstituted monovalent hydrocarbon groups, preferably having 1 to 10 carbon atoms, especially 1 to 6 carbon atoms, for example, alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, pentyl, neopentyl, hexyl, cyclohexyl, octyl and decyl; alkenyl groups such as vinyl, allyl, propenyl and butenyl; aryl groups such as phenyl and tolyl; and aralkyl groups such as benzyl and phenylethyl. Also included are halo-substituted monovalent hydrocarbon groups in which some or all of the hydrogen atoms on the foregoing hydrocarbon groups are substituted with halogen atoms.
Letters a and b are positive numbers satisfying 0.001 xe2x89xa6axe2x89xa61, 1xe2x89xa6bxe2x89xa62.5 and 1xe2x89xa6a+bxe2x89xa63, and preferably 0.01xe2x89xa6a xe2x89xa60.1, 1.8xe2x89xa6bxe2x89xa62 and 1.85xe2x89xa6a+bxe2x89xa62.1. The number of silicon atoms in a molecule is an integer of 2 to 1,000, preferably 2 to 100, and more preferably 5 to 60. The number of functional groups R1 directly attached to silicon atoms in a molecule is an integer of at least 1, preferably 2 to 5, and most preferably 2.
Illustrative of the organopolysiloxane are organohydrogenpolysiloxanes of the following formula (6), and organopolysiloxanes containing amino, epoxy, hydroxyl or carboxyl groups of the following formula (7). 
In formulae (6) and (7), R2 is a substituted or unsubstituted monovalent hydrocarbon group like R2 in formula (3), preferably a methyl or phenyl group; X is typically a monovalent hydrocarbon group containing an amino, epoxy, hydroxyl or carboxyl group, examples of which are the same as exemplified for R1 in formula (2). Letter p is desirably an integer of 0 to 98, especially 3 to 58, and q is desirably an integer of 0 to 20, especially 0 to 5.
Illustrative of the compounds of formulae (6) and (7) are the organopolysiloxanes shown below. It is noted that the number of recurring siloxane units in each formula is merely exemplary while it can be an arbitrary integer within the range corresponding to the above ranges of p and q. 
These organopolysiloxanes desirably have a molecular weight of 100 to 10,000 and especially 500 to 5,000, though not limited thereto. When the organopolysiloxane has a molecular weight in this range, a cured product of an epoxy or phenolic resin modified therewith does not undergo phase separation and remains uniform and thus possesses both the properties of silicone resins featuring flexibility and impact resistance and the properties of epoxy or phenolic resins featuring adherence, heat resistance and humidity resistance. The cured product may become rigid and brittle if the molecular weight is less than 100. Phase separation can occur if the molecular weight is more than 10,000.
The organopolysiloxane is desirably used in such an amount that the content of the organopolysiloxane component in the silicone-modified resin may be up to 80% by weight, although the amount of the organopolysiloxane used is not critical.
Any of well-known methods may be used in obtaining the silicone-modified epoxy or phenolic resin. Preferably the modified resin is obtained by effecting hydrosilylation addition reaction between alkenyl groups in the alkenyl group-containing epoxy resin or alkenyl group-containing phenolic resin and SiH group(s) in the organopolysiloxane having at least one hydrogen atom attached to a silicon atom (SiH group), i.e., organohydrogenpolysiloxane.
The resin composition of the invention requires that the organopolysiloxane component do not form a phase separation structure in the cured product, that is, the cured product be uniform. The factors that govern phase separation include the content of the organopolysiloxane component in the silicone-modified resin (specifically silicone-modified epoxy resin or silicone-modified phenolic resin), and the content of the organopolysiloxane component in the entire organic resin components (i.e., silicone-modified epoxy resin, silicone-modified phenolic resin and optional epoxy resin and/or phenolic resin to be described later, together) in the resin composition.
The content of the organopolysiloxane component in the silicone-modified epoxy resin or silicone-modified phenolic resin is desirably up to 80% and especially up to 70% by weight. If this content is more than 80% by weight, the organopolysiloxane component may form a phase separation structure in the silicone-modified resin, which becomes heterogeneous. If this silicone-modified resin is included in a resin composition, the organopolysiloxane component may still form a phase separation structure in the resin composition, which becomes heterogeneous. As a result, the flexibility and impact resistance characteristic of silicone resins are maintained due to the increased content of the organopolysiloxane component, but the adherence, heat resistance and humidity resistance characteristic of epoxy or phenolic resins are lost. The lower limit of the organopolysiloxane component content is preferably at least 10%, more preferably at least 20%, and even more preferably at least 30% by weight, thought not critical. If the content of the organopolysiloxane component is too low, it may become difficult to control the content of the organopolysiloxane component in the entire organic resin components to fall in an appropriate range.
The content of the organopolysiloxane component in the entire organic resin components (i.e., silicone-modified epoxy resin, silicone-modified phenolic resin and optional epoxy resin and/or phenolic resin to be described later, together) in the resin composition is preferably at least 10%, more preferably at least 20%, and even more preferably at least 30% by weight. If this content is less than 10% by weight, the organopolysiloxane component may form a phase separation structure in the resin composition, which becomes heterogeneous. As a result, the adherence, heat resistance and humidity resistance characteristic of epoxy or phenolic resins are maintained due to the reduced content of the organopolysiloxane component, but the cured product becomes rigid and brittle and loses the flexibility and impact resistance characteristic of silicone resins. The upper limit of the organopolysiloxane component content in the entire organic resin components is preferably up to 80% by weight for the same reason as described for the content of the organopolysiloxane component in the silicone-modified resin, though not critical.
No particular limits are imposed on the viscosity and epoxy equivalent of the silicone-modified epoxy resin or the viscosity and phenolic hydroxyl equivalent of the silicone-modified phenolic resin. Depending on a particular application, the modified resin may have any desired viscosity ranging from liquid to solid at room temperature. For resin compositions which are liquid at room temperature, the silicone-modified epoxy resin should preferably have a viscosity of 0.01 to 100 Paxc2x7s at 25xc2x0 C., especially 0.1 to 20 Paxc2x7s at 25xc2x0 C., and an epoxy equivalent of 100 to 2,000, especially 200 to 1,000. Similarly for liquid resin compositions, the silicone-modified phenolic resin should preferably have a viscosity of 0.01 to 200 Paxc2x7s at 25xc2x0 C., especially 0.1 to 100 Paxc2x7s at 25xc2x0 C., and a phenolic hydroxyl equivalent of 100 to 2,000, especially 200 to 1,000.
In the resin composition, it is preferred to use a mixture of the silicone-modified epoxy resin and the silicone-modified phenolic resin.
The amounts of the silicone-modified epoxy resin and the silicone-modified phenolic resin blended in the resin composition are not critical. Desirably, these modified resins are desirably blended in such a proportion that the content of the organopolysiloxane component in the entire organic resin components (i.e., silicone-modified epoxy resin, silicone-modified phenolic resin and optional epoxy resin and/or phenolic resin to be described later, together) in the resin composition may be at least 10% by weight. The cured product may become rigid and brittle if the organopolysiloxane component content is less than 10% by weight.
In the resin composition, any of well-known epoxy and phenolic resins may be included in addition to the silicone-modified resin.
The epoxy resin used herein is not critical with respect to molecular structure and molecular weight as long as it has at least two epoxy groups in a molecule. Any of conventional well-known epoxy resins may be used. Illustrative examples of useful epoxy resins include bisphenol-type epoxy resins such as bisphenol A epoxy resin and bisphenol F epoxy resin, novolac-type epoxy resins such as phenolic novolac epoxy resin and cresol novolac epoxy resin, triphenolalkane-type epoxy resins and polymers thereof such as triphenolmethane epoxy resin and triphenolpropane epoxy resin, epoxy resins having a biphenyl skeleton, epoxy resins having a naphthalene skeleton, dicyclopentadiene-phenol novolac resins, phenolaralkyl type epoxy resins, glycidyl ester type epoxy resins, alicyclic epoxy resins, heterocyclic epoxy resins, and halogenated epoxy resins. These epoxy resins may be used singly or as mixtures of two or more thereof.
The phenolic resin used herein is preferably selected from phenolic resins having at least two phenolic hydroxyl groups in a molecule. Illustrative examples include bisphenol type resins such as bisphenol A resin and bisphenol F resin, novolac resins such as phenol novolac resin and cresol novolac resin, triphenolalkane type resins such as triphenolmethane resin and triphenolpropane resin, resole type phenolic resins, phenol aralkyl resins, biphenyl type phenolic resins, naphthalene type phenolic resins, and cyclopentadiene type phenolic resins. These phenolic resins may be used singly or as mixtures of two or more thereof.
The amounts of the epoxy resin and phenolic resin blended are determined in consideration of the silicone-modified resin. The resins are preferably blended such that the molar ratio of epoxy groups in the silicone-modified epoxy resin and the epoxy resin to phenolic hydroxyl groups in the silicone-modified phenolic resin and the phenolic resin may fall in the range: 0.8xe2x89xa6(epoxy groups)/(phenolic hydroxyl groups)xe2x89xa61.25, and especially 0.9xe2x89xa6(epoxy groups)/(phenolic hydroxyl groups)xe2x89xa61.1. If this molar ratio is outside the range, some of the resins are left unreacted, which can interfere with the properties of cured products and hence, adversely affect the performance of semiconductor devices sealed therewith.
In the resin composition of the invention, a curing accelerator is preferably used.
Any desired curing accelerator may be used insofar as it can accelerate curing reaction of the silicone-modified epoxy resin and epoxy resin with the silicone-modified phenolic resin and phenolic resin. For example, one or more compounds selected from among imidazole compounds, tertiary amine compounds and organophosphorus compounds may be used as the curing accelerator. Of these, organophosphorus compounds are preferred for moisture-proof reliability.
Examples of suitable imidazole compounds include 2-methylimidazole, 2-ethylimidazole, 4-methylimidazole, 4-ethylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 2-phenyl-4-hydroxymethylimidazole, 2-ethyl-4-methylimidazole, 1-cyanoethyl-2-methylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, and 2-phenyl-4,5-dihydroxymethylimidazole.
Suitable tertiary amine compounds include amine compounds having alkyl or aralkyl substituents bonded to the nitrogen atom, such as triethylamine, benzyldimethylamine, benzyltrimethylamine and a-methylbenzyldimethylamine; cycloamidine compounds or organic acid salts thereof, such as 1,8-diazabicyclo[5.4.0]undec-7-ene and its phenol, octanoic acid and oleic acid salts; and salts or complex salts of cycloamidine compounds with quaternary boron compounds, such as the compound of the following formula. 
Suitable organophosphorus compounds include triorganophosphines such as triphenylphosphine, tributylphosphine, tri(p-methylphenyl)phosphine, tri(nonylphenyl)phosphine and triphenylphosphine triphenylborane; and quaternary phosphonium salts such as tetraphenylphosphonium tetraphenylborate.
An appropriate amount of the curing accelerator added is up to 10 parts (0 to 10 parts), desirably 0.1 to 10 parts, more desirably 0.5 to 5 parts by weight, per 100 parts by weight of the entire organic resin components (i.e., silicone-modified epoxy resin, silicone-modified phenolic resin and optional epoxy resin and/or phenolic resin to be described later, together). With less than 0.1 part by weight of the curing accelerator, the resin composition may become under-cured. More than 10 parts by weight of the curing accelerator may detract from the storage stability of the resin composition.
Depending on a particular application, inorganic fillers such as silica, alumina, talc, mica, silicon nitride, boron nitride and silver, flame retardants, ion trapping agents, wax, colorants, adhesive aids and the like may be added to the resin composition of the invention insofar as they do not compromise the objects of the invention.
The resin composition of the invention can be obtained by mixing the respective components in a well-known manner. For example, the silicone-modified epoxy resin, the silicone-modified phenolic resin, and optionally, the epoxy resin, phenolic resin, curing accelerator, inorganic filler and other components are simultaneously or separately agitated, dissolved, mixed and dispersed while heating them if necessary. The means for mixing these components may be a mixer if the resin composition is pasty, or a roll mill or extruder if the resin composition is solid. The order of mixing and other conditions including time, temperature, and pressure may be properly selected so as to obtain the desired resin composition.
The viscosity of the resin composition is not critical and may be properly set, depending on a particular application, in a wide range covering from solid to liquid at room temperature. In particular, liquid resin compositions preferably have a viscosity of 10 to 1,000 Pass at 25xc2x0 C.
The inventive resin composition is advantageously used in coating and sealing surfaces of semiconductor chips. Although the type of semiconductor device is not critical, the resin composition is useful in the application of bonding hard chips to flexible substrates such as chip on board (COB) and chip on flex (COF).
Conventional methods and conditions may be used in coating and sealing surfaces of semiconductor chips with the inventive resin composition. Preferred heat curing conditions include 80 to 200xc2x0 C. and 30 to 300 minutes.
For the resin composition of the invention, it is requisite that the organopolysiloxane component do not form a phase separation structure in the cured product, that is, the cured product be uniform. Whether or not the organopolysiloxane component is uniform in the cured product is judged by its outer appearance. The cured product is uniform if it looks clear and non-uniform if it looks opaque.
The inventive resin composition cures into a product having significantly improved flexibility and impact resistance without detracting from adherence, heat resistance and humidity resistance inherent to conventional well-known semiconductor-encapsulating resin compositions. At the bonding interface between parts having noticeably different mechanical and thermal behaviors, the resin composition can fully absorb and alleviate the stresses induced therebetween.